This invention relates to apparatus for sensing the position of an object movable along a prescribed path within limited boundaries. More particularly, this invention relates to apparatus of the aforementioned type wherein an optoelectronic position-sensitive detector (PSD) and a light source are disposed within a housing, the light source providing a light beam directed onto the PSD and movable in response to movement of a mechanical operator extending through the housing to be in contact with the object.
In industrial control applications, it is often desirable to monitor excursions of an object or objects from a normal path or position. Such monitoring is commonly accomplished with photoelectric, ultrasonic or electromagnetic proximity sensors operating in a non-contact mode with the object. However, some industrial process control environments are not well suited for such sensors because they contain a large amount of pollutants or contaminants or electrical noise. In such applications, and where the objects are capable of withstanding physical contact by a sensor, an enclosed switching apparatus having a mechanical operator in contact with the objects can be utilized. Photoelectric switches and photodiode arrays have been utilized within such devices to provide a hybrid mechanical-photoelectric sensor. The photoelectric switch is a digital device which does not lend itself to applications desiring to continuously monitor a changing position. Photodiodes or phototransistors may be used, but the range in output signals for these devices from fully illuminated to fully blocked is objectionably small. Photodiode arrays have been used, but these detectors require a costly multiplexing circuit inasmuch as the individual diodes are sequentially read and their outputs are related to a timing sequence in the multiplexing circuit.
While the sensors described hereinbefore are each suitable for particular applications, this invention relates to improvements thereover.